Linear and cyclic amphiphilic peptides, (W4KR5) and [W4KR5], were evaluated as antibacterial agents against Gram-positive and Gram-negative bacteria, including four multi-drug resistant strains and the corresponding four non-resistant strains. Cyclic peptide [W4KR5] showed higher antibacterial activity than the linear (W4KR5) counterpart. Cyclic [W4KR5] was subjected to combination (physical mixture or covalent conjugation) with meropenem as a model antibiotic to study the impact of the combination on antimicrobial activity. A physical mixture of meropenem and [W4KR5] showed synergistic antibacterial activity against Gram-negative P. aeruginosa (ATCC BAA-1744) and P. aeruginosa (ATCC 27883) strains. [W4KR5] was further subjected to extensive antibacterial studies against additional 10 bacteria strains, showing significant antibacterial efficacy against Gram-positive bacteria strains. Combinations studies of [W4KR5] with an additional 9 commercially available antibiotics showed significant enhancement in antibacterial activity for all tested combinations, especially with tetracycline, tobramycin, levofloxacin, clindamycin, daptomycin, polymyxin, kanamycin, and vancomycin. Time-kill kinetics assay and flow cytometry results exhibited that [W4KR5] had a time-dependent synergistic effect and membrane disruption property. These data indicate that [W4KR5] improves the antibacterial activity, presumably by facilitating the internalization of antibiotics and their interaction with the intracellular targets. This study introduces a potential strategy for treating multidrug-resistant pathogens by combining [W4KR5] and a variety of classical antibiotics to improve the antibacterial effectiveness.
Keywords: Combination therapy; Covalent conjugate; Cyclic peptide; E. coli; FACS Meropenem; Multi-drug resistant strains.
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